Yes, its true. I have an '04 10in L7 in a custom box mounted on the rear deck of my miata. It is powered by a power acoustik 980/2 bridged to 1 channel. The sub hits but not any more then my friends 2 10" duals. My question is if the sub is rated at 600rms/1200 peak, can i run a 1000 watt mono 1 ohm stable amp w/o having to worrying about blowing the sub?? I bought the kicker for a reason and the fact that my friend can spend 60 bucks at pepboys and still get as good sound irritates the crap outta me.
that sub will handle much more than 600 rms, even much more than 1000. but!, only for short periods of time. go ahead and buy that 1000 watt amp and bump it but do not run it for more than a 10 - 15 seconds, it will blow up. my subs are rated at 2500rms but i burp them with 12000rms. as long as you give the woofer time to cool down you'll be fine, just keep a keen ear of how your woofer is sounding, if its distorting then of course turn it down. just be carefull with excess wattage, if your not paying attention you could easily have it up to loud and smoke your sub.
your might sound louder because there is more room in his cabin so he can push more air. lets face it miata arent known for there spacious leg room or any room at that. tiny car and so it is hard to get big numbers out of it. i hope you are not a big guyt or getting in and out of that car would be a pain.
yea your best bet would probably be to just stick with you have, granted he has dual subs he's also for one moving more air then you are with 2 10"s as well as he's getting the cabin gain that you arent. miata's arent know for there spacious cabin, with the same box and power you sub will sound alot different in an SUV then in your little miata...